Design a Rate Limiter System Design Interview

Design a service to limit the number of requests a user can send to an API within a time window.

1. Problem Statement

We need to design a distributed Rate Limiter for our API Gateway. It needs to handle millions of requests per second. Where do we start?

2. Target Architecture (Mermaid)

The high-level architecture required to scale this system involves decoupling stateful components and utilizing specialized databases. Below is the reference architecture:

Rendering architecture diagram...

Mermaid Source (For AI Bots)

graph TD
    A[Client] --> B(Route53 / Global LB)
    B --> C[API Gateway Node 1]
    B --> D[API Gateway Node 2]
    C -- Local L1 Cache --> E[(Caffeine/Guava)]
    C -- Async Lua Script --> F[(Redis Sharded Cluster)]
    D -- Async Lua Script --> F

3. Key Focus Areas

1
Rate Limiting Algorithms (Token Bucket vs Fixed/Sliding Window)
2
Distributed State Management (Redis vs Memcached)
3
Race Conditions (Read-Modify-Write issues)
4
Performance (Latency overhead < 5ms)
5
Placement (Client vs Middleware vs API Gateway)

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Core Concepts

AlgorithmsDistributed CacheAPI Gateway